Antibody therapies represent an ever increasing segment of the global pharmaceutical market. Approved antibody-based products include treatments for cancer, autoimmune disorders (e.g. rheumatoid arthritis), infectious diseases, cardiovascular disease and many other disorders. However, to improve patient outcomes, perturbation of multiple therapeutic targets or biochemical pathways is often desired. In this context, antibody therapy has limitations.
Co-administration of two or more antibody therapies requires multiple injections or, alternatively, a single injection of a co-formulation of two different antibody compositions. While multiple injections permit flexibility in dose and timing of administration, the inconvenience and discomfort associated with multiple injections may reduce patient compliance. While a co-formulation of multiple antibody agents would permit fewer injections, the difficulty and/or expense associated with designing a suitable pharmaceutical formulation that provides the necessary stability and bioavailability, for each antibody ingredient, may be prohibitive. Further, any treatment regime which entails administration of separate antibody agents will incur added manufacturing and regulatory costs associated with the development of each individual agent.
Bispecific antibodies (BsAbs)—single agents capable of binding to two distinct antigens or epitopes—have been proposed as a means for addressing the limitations attendant with co-administration or co-formulation of separate antibody agents. BsAbs integrate the binding activities of two separate antibody therapeutics into a single agent, thus providing a potential cost and convenience benefit to the patient. In some circumstances, BsAbs may also elicit synergistic or novel activities beyond what an antibody combination can achieve.
Recombinant DNA technologies have enabled the generation of multiple BsAb formats. For example, single chain Fv (scFv) fragments composed of antigen recognition domains (i.e., heavy chain variable (VH) and light chain variable (VL) domains) tethered by flexible or structured linkers, taken from existing monoclonal antibody (MAb) therapeutics or discovered by in vitro screening methodologies, have been used as building blocks for BsAb generation. In this context, an scFv fragment(s) which binds a particular antigen can be linked to another moiety, for example a separate scFv or an IgG MAb which binds a separate antigen, to form multi-valent BsAb. However, a limitation with the use of scFvs is that they lack the archetypical Fab architecture which provides stabilizing interactions of the heavy chain (HC) and light chain (LC) constant domains (i.e., CH1 and CL, respectively) which can improve thermal stability or solubility, or reduce the potential for aggregation.
The ability to generate bispecific antibodies retaining the full IgG antibody architecture has long been a challenge in the field of antibody engineering. One approach for generating fully IgG bispecific antibodies entails co-expression of nucleic acids encoding two distinct HC-LC pairs which, when expressed, assemble to form a single antibody comprising two distinct Fabs. However, to achieve efficiency in manufacturing, each of the expressed polypeptides of the distinct HC-LC pairs must assemble with its cognate polypeptide with good specificity to reduce generation of mis-matched Fab by-products. In addition, the two distinct HCs must heterodimerize in assembly to reduce generation of mono-specific antibody by-products. Fab interface designs which promote assembly of particular HC-LC pairs have recently been described. (See Lewis, et al. (2014), Nat. Biotechnol., 32; 191-198; and Published PCT Applications WO2014/150973 and WO2014/0154254) in addition, procedures for directing assembly of particular HC-HC pairs by introducing modifications into regions of the HC-HC interface have also been disclosed in the art. (See Klein et al., mAbs; 4(6); 1-11 (2012); Carter et al., J. Immunol. Methods; 248; 7-15 (2001); Gunasekaran, et al, J. Biol. Chem.; 285; 19637-19646 (2010); Zhu et al., Protein Sci.; 6: 781-788 (1997); and Igawa et al., Protein Eng. Des. Sel.; 23; 667-677 (2010)). However, there remains a need for alternative methods for generating fully IgG BsAbs.